In recent years, as computers have developed and become popular, various kinds of information are put into digital data. As a device for storing such digital data, there is a storage device such as a magnetic tape and a magnetic disk. Because data to be stored has increased day by day and the amount thereof has become huge, a high-capacity storage system is required. Moreover, it is required to keep reliability while reducing the cost for storage devices. In addition, it is required that data can be easily retrieved later. As a result, such a storage system is desired that is capable of automatically increasing the storage capacity and performance thereof, that eliminates a duplicate of storage to reduce the cost for storage, and that has high redundancy.
Under such a circumstance, in recent years, a content address storage system has been developed as shown in Patent Document 1. This content address storage system distributes data and stores into a plurality of storage devices, and specifies a storing position in which the data is stored based on a unique content address specified corresponding to the content of the data.
To be specific, the content address storage system divides predetermined data into a plurality of fragments, adds a fragment as redundant data thereto, and stores these fragments into a plurality of storage devices, respectively. Later, by designating a content address, it is possible to retrieve data, namely, a fragment stored in a storing position specified by the content address and restore predetermined data before divided from the plurality of fragments.
Further, the content address is generated so as to be unique corresponding to the content of data. Therefore, in the case of duplicated data, it is possible to acquire data of the same content with reference to data in the same storing position. Thus, it is not necessary to separately store duplicated data, and it is possible to eliminate duplicated recording and reduce the data capacity.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. JP-A 2005-235171
As mentioned above, the content address storage system divides predetermined data into a plurality of fragments and stores the fragments into a plurality of storage devices, respectively. Even if commands to store data are given by a plurality of hosts, the content address storage system stores the data into the storage devices in the received order.
Therefore, there is a case that data received from a specific host and data received from various hosts are alternately stored in the storage devices. Consequently, at the time of retrieving a set of data received from the specific host, or at the time of simultaneously retrieving and cashing data and following data, it is difficult to retrieve the related data together. In other words, since data received from the plurality of hosts may be stored into the respective storage devices in the mixed order, it is impossible to retrieve related data together and it is impossible to realize efficient data retrieval in this case. As a result, such a problem arises that it is impossible to increase a retrieval speed and it is impossible to increase the performance of the storage system.